Catalytic cracking process and apparatus



Oct. 16, 1956 T. RICE 2,767,126

CATALYTIC CRACKING `PROCESS AND APPARATUS Filed Marph 2s, 195s UnitedStates Patent CATALYTIC CRACKING PROCESS AND APPARATUS Theodore Rice,Penn Township, Allegheny County, Pa., assignor to Gulf Research &Development Company, Pittsburgh, Pa., a corporation of DelawareApplication March 23, 1953, Serial No. 344,078

11 Claims. (Cl. 196-52) This invention relates to a uid catalyticcracking process and apparatus and more particularly to an improvedprocess and apparatus for the catalytic conversion of hydrocarbons.

Hydrocarbon charge stocks containing appreciable amounts of deleteriousmaterials, such as sulfur compounds and/or nitrogen bases, are notordinarily desirable as charge stocks for conventional catalyticcracking operations because these charge stocks, under conventionalcatalytic cracking conditions, normally tend to deposit upon thecracking catalyst excessive amounts of catalyst contaminant. Thecatalyst deposits tend to build up on the cracking catalyst at analarming rate, with the result that the cracking catalyst may quickly bepoisoned and the cracking reaction adversely aected or the crackedproducts may be contaminated with the undesirable contaminants.

In accordance with the invention, a hydrocarbon charge stock containingappreciable amounts of deleterious materials, such as sulfur compoundsand/ or nitrogen bases, is contacted in a tirst reaction zone underrelatively mild cracking conditions with partially regenerated uidizedcracking catalyst obtained from an upper portion of a regeneration Zone;and a hydrocarbon charge stock substantially free of objectionablematerials, such as sulfur compounds and/or nitrogen bases, and whichmay, in fact, comprise the cracked products comprising the eiuent fromthe iirst reaction zone, is contacted in a second reaction zone underconventional cracking conditions with regenerated tiuidized crackingcatalyst obtained from a lower portion of said regeneration zone.

By operating in accordance with my invention, the above-notedditiiculties are avoided by removing in the rst reaction zone,maintained under relatively mild cracking conditions, the objectionablematerials from such a charge stock, and thereafter passing the remainderor" the charge stock to a second reaction zone where conventionalcatalytic cracldng conditions are maintained. When the charge oilcontains large amounts of sulfur, H28 vapors are released and heavycombustible deposits not vaporized are deposited on the crackingcatalyst in the first reaction zone. Since the HzS vapors pass overheadfrom the rst reaction Zone and may be detrimental to natural catalystsin subsequent cracking operations, it may be advisable to remove HzSvapors from the etiiuent. This can be done by means known in the art, asfor example, by passing the effluent carrying the H28 vapors through avapor-liquid separator. Treating charge stocks containing large amountsof nitrogen bases in the first reaction zone will result inrdeposits ofcombustible nitrogen-containing compounds on the cracking catalyst andsome formation of nitrogen and ammonia vapors. ri`he nitrogen andammonia vapors are not detrimental to subsequent cracking operations andneed not be removed from the eiuent in the rst reaction zone. When thecharge stock contains both sulfur and nitrogen compounds, volatileproducts as well as combustible deposits containing both of thesecompounds are formed in the iirst reaction zone. For simplicity, thesecombustible deposits resulting from the cracking of the deleteriouscompounds noted, in particular sulfur compounds and/ or nitrogen bases,as well as the combustible hydrocarboi naceous deposits generally formedon the catalyst during catalytic cracking, sometimes known `as coke,will be termed hereinafter contaminant Y it is important in the practiceof my invention that (l) cracking catalyst employed in the firstreaction zone, wherein mild cracking conditions are maintained, bepartially regenerated cracking catalyst obtained from the upper portionof the regenerator; (2) cracking catalyst employed in the second 'orconventional catalytic'cracking zone be regenerated cracking catalystobtained from a lower portion of said regenerator; (3) spent catalystfrom each of the reaction Zones be continuously passed to the upper partof said regenerator; and (4) an oxidizing gas, like air, be passedupwardly through the base of the regenerator for the purpose ofregenerating the catalyst therein.

By operating in this manner, and, as will be explained in detm'lhereinafter, as the catalyst moves downwardly from the upper portion ofthe regenerator and is regenerated by the oxidizing gas moving upwardly,the oxygen in the oxidizing gas is substantially consumed with theresult that the gas in the uppermost portion of the regenerator containslittle or no oxygen and after-burning is avoided.

in obtaining partially regenerated catalyst from an upper zone of theregenerator for the first reactor and regenerated catalyst from a lowerzone of the regenerator for the second reactor, an etcient and reliablemeans of obtaining sumcient amounts of the proper catalyst for each ofthe reaction zones is assured. Since the cracking catalyst passed to thetirst reaction zone is to be employed under relatively mild crackingconditions only, and thus need not be unduly active, it is apparentthat, by obtaining partially regenerated catalyst from the upper part ofthe regeneration zone, I am able to control the supply of such catalystas well as the level of the contaminant thereon. Similarly, the catalystneeded in the second or conventional catalytic cracking Zone ispreferably a relatively active cracking catalyst substantially free ofcontarninant, and by obtaining the catalyst for such latter Vzone from alower portion of the regenerator I am able to control the amount andquality of catalyst passed t0 such latter zone. Y

The novel apparatus employed in carrying out my process comprises aregenerator provided with a plurality of regeneration Zones, superposedone upon another; a iirst and second reactor; means for removing apartially regenerated uidized cracking catalyst from one of the upperregeneration zones, admixing it with a charge stock containingappreciable amounts of objectionable materials, such as theaforementioned sulfur compounds and/ or nitrogen bases, and moving theresulting mixture to the rst reactor; means for removing a regeneratedtluidizing cracking catalyst from one of the lower regeneration zones,admixing it with a charge stock containing substantially lessobjectionable materials than are present in the charge stock passed tothe rst reactor, and moving the resulting mixture to the second reactor;means for removing cracked products from each of the two reactors; andmeans for continuously recycling catalyst contaminated with carbonaceousmaterial from each of the two reactors to the regenerator.

Any conventional cracking catalyst, natural or synthetic, can beemployed in the process of my invention, as for example silica-aluminacracking catalyst comprising an acid-activated halloysite such asFiltrol SR, montmorillonite clay such as Filtrol D, syntheticsilica-alumina cracking catalyst such as synthetic composites containing3 between 80 to 90 percent of silica and 10 to 2O percent of alumina,and so forth. The aforementioned catalysts should be of conventionalparticle size used in iuid catalytic cracking systems. Y n u ln ordertoV illustratethe process and apparatusrof my invention, referenceshould be had to the accompanying 'figure which is aV diagrammaticrepresentation-of a fluid `-conversionsystem in accordance with myinvention. The accompanying ligure is hereby incorporated into myinvention and made a part thereof. Y A charge stock comprising a heavygas oil containing iappreciable amounts of sulfur compounds and/o1'nitrogen bases is introduced into the system through line 12. ThechargeV stock has been preheated (by means not shown) to atemperature'rsomewhat below the cracking Y temperature maintained inreactor 22.Y If desired, the charge stock in line V12 can be joined byrecycle oil from line 13. The combined feed enters line ,14 and isjoined therein by partially regenerated cracking catalyst particles,such as silica-alumina cracking catalyst, entering through valve i6`from standpipe 18 extending upwardly through the Vbase of regenerator20 into upper portion A thereof.- The partially Vregenerated crackingcatalystV entering standpipe 18 is at a temperature somewhat above theVcracking temperature present in reactor 22 and serves to heat themixture of charge stock and recycle oil to this cracking temperature.The mixture of partially regenerated catalyst, charge stock and recycleoil, if any, passes upwardly through line 14 into the base of reactor22, `which contains a dense phase bed of silica-alumina crackingcatalyst particles.

Within reactor 22 the mixture passes through grid 24 and the feed ismildly cracked throughtcontact with the catalyst particles in reactor22. The dense phase uidized Vbedof catalyst particles within reactor 22is maintained at a temperature in the range of about 750 to about 900 F.and a pressure of about 15 pounds per square inch for a time suicient toobtain mild cracking of the total charge `and the release of a majorportion of the sulfur and/or nitrogen in the'charge in the form ofhydrogen suliide, combustible catalyst deposits, etc. The crackedproducts, together with the uncracked eiluent, are withdrawn fromreactor 22 ythrough cyclone separator 26, which returns entrainedcatalyst tothe dense phase catalyst bed in reactor 22, and; areledthrough line 28 to a ractionator '(not shown.) where theysubsequently undergo such addi- ,tional refining and processing as isreadily apparent to one skilled in the art. Y

The rate of introduction of feed and catalyst into reactor 22 and therate of withdrawal of products and contaminated catalyst from reactor 22is preferably so regulated that the average level of contaminant uponthe catalyst in reactor 22 is maintained preferably in the range ofabout 0.5 to about 1.2 percent by weight. The withdrawal of contaminatedcatalyst from reactor 22 is effected through stripper 30. Thecontaminated catalyst passes through stripper 30 or strippers of otherdesigns known to those familiar with the art, and is stripped ofentrained hydrocarbons by an inert gas such as steam entering stripper30 through steam line and nozzle 32.

From stripper 30 the contaminated catalyst passes through valve 34 andline 36 to regenerater 20. Regenerator is at a lower level than reactor22 so that iow from reactor22 to regenerator 20 can be readily effectedwithout the necessity of adding appreciable quantities of aerating gasto line 36. However, some aerating gas can be added to Vfacilitateproper flow of the contaminated catalyst from reactor 22 to regenerator20.

Regenerator 20 comprises a two-zone regenerator with upper zone'A beinglocated above a perforated'plate member or grid 40 and lower zone Bbeing located below grid 40.- The contaminated Vcatalyst from line 36enters zone AV and is regenerated by oxygen-containingregeneratinggas-leaving zone B. This oxygen-containing Yregeneratinggas, originally comprised an oxygen-rich gas,

lyst containing preferably in the rangeV of about 0.1 tol about 0.6weightper cent of contaminant. A Grid 40 re- Y distributes catalyst andlregenerating gas in their move-V ment through the regenerator and thusprovides a means for eliminating channeling and permitting intimatecontact betWeent-he catalystA andthe regeneratingV gas. In this waytemperatures throughout Vthe Vregenerator are easilymaintained at atemperature in the range 0f 950. to about ll25 F., and temperaturesabove about ll50 F., which may occur in conventional single-zoneregenerators because of hot spots and which mayV result in permanentdeactivation of the catalyst, are avoided. Redistribution, moreover,provides for rapid disengagement and removal of nitrogen gases and H28vapors that might have been occluded from reactor 22. The regenerationeffected in regeneration zone B is more severe than that eiected inregeneration zone A, and accordingly a major portion of the oxygencontent of the regenerating gas is consumed in regeneration zone B.

As a result'of the foregoing, the regenerating gasV enteringregeneration zone A has a relatively low concentraf tion of oxygen. Thisconcentration of oxygen should be suiicientV to insure that thecontaminant level on' the spent catalyst from reactor 22 and reactor 62,hereinafter noted, is reduced to a value of about 0.4 to about 1.0percent by Weight in regeneration zone A.

However,v the oxygen content of the regenerating gas in regenerationzone A should be sufficiently low, preferably less than about 2 percent,as to eliminate the danger of after-burning in the upper part ofregenerator 20.

After-burning can occur when a combustible mixture t exists in thesection of the regenerator known as the dilute phase, which is theregion above the more dense uid bed where the concentration of thecatalyst particles is relatively low. In the regeneration of Vthe spentcatalyst, the burning of the carbon results in the formation ofcombustion products such as carbon monoxide, carbon dioxide and waterand, in addition, any oxygen notwconsumed during regeneration is alsopresent. When' the'V oxygen and carbon monoxide are in the properproportions, the mixture is readily combustible. The gas may then burnin the top of the regenerator or in the flue gas ducts, resulting invery high temperature, above about 1100 F., which is extremely damagingto the cyclone separators and the ue gas ducts, and may Valso affect theactivity of the catalyst. After-burning can usually be avoided if theoxygen content of the combustion gas in the dilute phase of zone A iskept below about 2 percent.

By operating in accordance with my invention, the amount of oxygenpresent in the oxidizing gas in the `dilute phase of zone A is easilymaintained below about 2 percent. The oxidizing gas moving upwardly fromzone B mayV contain more than 2 percent oxygen but the excess oxygen, orthat amount :over 2 percent, is consumed in burning off combustible`deposits on the catalyst surface in zone A. Thus, by regenerating thecontaminated catalyst in the regenerator while maintaining the catalystinV a plurality-,of beds, the excess oxygen which would ordinarily bepresent in the upper portion lof the regenerator Y is substantiallyconsumed in an upper catalyst bed, and 'after-'burning is avoided. t e nThe regeneration ue gases yare Withdrawn fromV :re-

generator 20 through cyclone Aseparator 50 and line "52;V

yCyclone Iseparator 50 returns regenerating catalyst -to the dense phasefbed of catalyst in regenerator 20. Y

While standpipe 18 extends Yupwardly through the base of regenerator 20into upper 'zoneV A for the purposeof 'withdrawing partially regeneratedcatalyst preferably con- :taining about 0.4 rto about 1.0 Weight percentof contaminant -for use in reactor V2-2, a second standpipe 54 extendsupwardly through the base of regenerator 20 into` lower zone B for thepurpose of withdrawing regenerated catalyst containing preferably about0.1 :to about 0.6 weight percent of contaminant for Vuse 'in reactor 62,Where charge stocks containing little or no deleterious materials, IsuchYas objectionable -sulfur and/or nitrogen compounds, are caitalyticallycracked.

A charge stock comprising a heavy gas oil containing substantially less`of the deleterious materials present in the charge stock passed rtoreactor 22, which has previously been heated (by means not shown) to `atemperature somewhat below the cracking temperature maintained inreactor 62, is introduced into line 56. This charge `stock may bejoined, if desired, by recycle cil and/or desulfurized :oil through line57, particularly that obtained as a result of cracking in reactor 22.The combined charge in line 58 is joined by regenerated silicaaluminacracking catalyst containing preferably about 0.1 to about 0.6 `weightpercent of contaminant from standpipe 54 through valve 60. Theregenerated catalyst =from standpipe 54 is yat .a temperature somewhat@above the cracking temperature maintained in reactor 62 :and serves toheat the mixture `of total charge to this cracking tempera/ture. Themixture of regenerated catalyst and charge passes upwardly yfrom line 58into the base of reactor 62. Reactor 62 contains a dense phase bed ofsilica-alumina cracking catalyst particles.

Within reactor 62 the mixture passes through grid 64 and .the feed iscatalytically cracked through contact with the catalyst particles inreactor 62. The dense phase -uidized bed of catalyst particles withinreactor 62 is maintained at cracking temperatures in the range of labout800 lto `about llO0 F., such as about 900 F. As ya result of contactwith the catalyst particles in reactor 62 the feed is -catalyticallycracked to relatively low-boiling hydrocarbons ysuch as gasoline boilingrange hydrocarbons, butanes, butenes, propane fand propylene.Simultaneously, contaminant is deposited upon the silicaalumina crackingcatalyst. The cracked products `are withdrawn from reactor 62 throughcyclone separator 66, which returns entrained catalyst to the densephase catalyst bed in reactor 62, and the cracked products then passthrough line 2S, Where they join the products from reactor 22, to afractionator (not shown). If desired, the cracked products from reactor62 -may be :sent to a fractionator `other than that to which theproducts from reactor 22 are sent. In the fractionator, these crackedproducts undergo such additional refining and processing as is readilyapparent to lone skilled in the art.

The rate of introduction of feed and catalyst into reactor 62 and therate :and withdrawal of cracked products and contaminated catalyst fromreactor 62 preferably `are so regulated that the average level Lofcontaminant upon the catalyst in reactor 62 is maintained in the range`of about 0.5 to about 1.2 percent by weight. 'The withdrawal :ofcontaminated catalyst from reactor 62 is effected :through .stripper 68or strippers of other designs known to those familiar with the art. Thecontaminated catalyst passes through stripper I68 and is stripped ofentrained hydrocarbons by an incr-t gas such as steam entering stripper68 through steam line Iand nozzle 70.

From stripper 68 fthe contaminated catalyst passes through valve 72 'andline 74 to regenerator 20. Regenerator 20 is at `a lower level thanreactor 62 so that flow from reactor 62 to regenerator 20 can be readilyelected without the necessity of adding appreciable quantities ofaora-ting gas to line 74. However, 'some aerating gas can be added tofacilitate proper ow of the contaminated catalyst from reactor 62 toregenerator 20. Operating conditions in regenerator 20 are maintained|as previously described.

In order to illustrate a .specific embodiment in accordis contacted withcracking catalyst in reactor 22 iat `a temperature in the range oflapproximately 750 to ab out 900 F. and 4a pressure of about 15 pound-sper square inch gauge for a time sulicient to obtain mild crackingtherein. As a result of such cracking, substantially rall of thedesirable gas 'oil fractions :are vaporized .and the heavy cornponentsof the gas oil charge are mildly cracked, resulting in it'ne formationof lighter hydrocarbons, which are removed from the reactor along withthe vapor-ized gas oil fractions, and deposits of heavy combustiblematerial on the catalyst therein.

ln reactor 62, a gas toil charge stock, relatively free .of deleteriousmaterials found in the charge stock entering reactor 22, and having thefollowing inspection data:

Characterization factor 11.8 ASTM distillation, F. (D-158):

Initial boiling Vpointdend point 60G-1050 is catalytically cracked atatemperature of about 900 F. :and a pressure about 15 pounds per squareinch gauge, while maintaining a catalyst to oil ratio of about 10:1 'andla 'space velocity of about 1.5 (weight per hour of oil per weight :ofcatalyst). As Ia result tof cracking in reactor 62, relativelylow-boiling hydrocarbons such #as gasoline boiling range hydrocarbons,butanes, butenes, propane and prepylene ,are :obtained in the eiiluenttherefrom land carhfonaceous contaminant is deposited on the crackingcatalyst.

While l have disclosed specific operating conditions which arepreferably maintained in reactors 22 and 62, it is understood that theseconditions are to be considered illustrative only and not limitative.The operating conditions necessary in practicing my invention are notcritical but may be varied over a wide range and may be considered to bedependent yon many variables, such as the composition of the chargestocks employed, the cracked products desired, a balance of economiccosts involved, and so forth. For example, in reactor 22, thetemperature may vary from about 700 to about 1000 F., the pressure fromabout atmospheric to pounds per square inch gauge or more but preferably.at atmospheric pressure, and the space velocity may range from about 5to l5; while in reactor 62 the temperature may range from about 800u toabout 1l00 F., the pressure from about atmospheric to about 100 poundsper square inch gauge or more, and the space velocity may range fromabout 0.5 to about 10 or more. lt has been found that the poisoningeffect of H28 is a function of its partial pressure and time of contact.Therefore, it is preferred to operate at low pressures and high spacevelocities in reactor 22 to minimize deactivation of the catalyst. Thecatalyst oil ratio employed in reactors 22 and 62 may be as low las 1:1or as high as 15:1 4or more.

'While the character of the invention has been described in detail andexamples given, this has been done by way of illustration only, and theinvention is not t-o be considered to be so limited. Numerousmodifications and variations of my invention may be apparent to oneskilled in the art, and these modicati-ons should be construed asincluded within the scope of the claims appended hereto. For example,stan-dpipes 18 and 54 need not be located as shown in the drawing butmay penetrate the base of regenerator 20 at other points as well, and,in fact, may even run exteriorly of regenerator 20 Ybefore penetratingzones A and B, respectively. If desired, regenerator 20 may be locatedat a higher level than either of reactors- 22 andj 62,.-or both, andadditional aerating gas maybe introduced into lines 36and 74 for thepurpose of'aiding the movement `of spent catalyst fromir'reactors 22 and62 to regenerator 20. in addition, the regenerator may include ymorethan Vtwo regenerator zones ifdesired.

The fluid'catalytic process and apparatus of my invention permit Ytheprocessing of distillates having lan appreciable amount of deleteriousmaterials, such as sulfur compounds and/or nitrogen bases, withoutmaterially aiecting the activity of the cracking catalyst employed intheconventional catalytic cracking zone and at the same time permit higheryield of valuable low boiling point hydrocarbons Yto be obtained whilesimultaneously decreasing both the deposition of undesirable contaminantupon'the catalyst in said cracking zone and the yield of undesirable lowboiling point, gaseous hydrocarbons.

While I have described my invention by reference to certain improvementsthereof, the same is not limited thereto except as deiined by theappended claims.

I claim:

A iluid catalytic cracking process which comprises regeneratingcontaminated fluidized cracking catalyst particles by removing thecontaminant by oxidative combustion from the catalyst particles in aregenerator provided with a plurality of regeneration zones, superposedone upon another; in which the amount of contaminant present on thecracking catalyst in an upper zone is greater than that which is presenton the cracking catalyst in arlower zone thereof, the amount ofcontaminant in said upper zone being about 0.4 to about 1.0 weightpercent .and the amount `of contaminant in said lower Zone being about0.1 to about 0.6 weight percent; admixing a hydrocarbon charge. stockcontaining-appreciable amounts of deleterious materials with partiallyregenerated cracking catalyst obtained from an upper regeneration zone;subjecting such mixture to relatively mild.

cracking conditions in a rst reaction zone for .a time sufficient to-release a major portion of said deleterious materials in said iirstreaction zone and deposit contaminant on the cracking catalyst therein;admixing a hydro-V carbon charge stock containing substantially less ofthe deleterious materials than is present in the charge stock passed toiirst reaction zone with a regenerated cracking catalyst obtained from alower regeneration zone; subjecting said last named mixture to elevatedtemperatures in `a Vsecond reaction zone, thereby forming a relativelylower boiling hydrocarbon product and depositing contaminant on thecatalyst particles therein; continuously recycling contaminated catalystfrom each of the two reaction zones to the regenerator and continuouslywithdrawing the cracked product from each of the two reaction zones.

2. A process in accordance with claim 1 in which the charge stockentering the iirst reaction zone contains appreciable -amounts ofdeleterious sulfur and nitrogencontaining compounds.

3. A process in accordance with claim 1 in which the charge stockentering the rst reaction zone contains appreciable amounts ofdeleterious sulfur-containing compounds. Y

4. A process in accordance with claim ,1 in which the charge stockentering the first reaction Zone contains appreciable amounts ofdeleterious nitrogen-containing compounds.

aoK

5. A process Ain accordance with claim '1; in which the chargeY stockentering Vtheecond reaction zone; comprises theefliuent from the irstreaction zojne. y

`6.1A process in accordanceA with claim 1 in which. an oxygen-containinggas is 'passed `upwardly through the regenerator and the catalystV beingregenerated in passed downwardly through 'the regenerator.

g 7. A iluidV cracking unit comprising a regenerator provided with aplurality of regeneration zones, superposed one upon another; means forseparating an upper regeneration zone from a lower regeneration zone andpermitting movement of catalyst and regenerating gas there-V through; areactor;-means for removing a partially regenerated fluidized crackingcatalyst from an upper regeneration zone, admixing it with a hydrocarboncharge stock, moving Vthe resulting mixture to the reactor; Vmeans forremoving cracked products from the reactor; means for removing aregenerated iluidized cracking catalyst from a lower regeneration zone;means for continuously recycling contaminated catalyst from the reactorto` an upper regeneration zone; and means for introducing anoxygenfcontaining gas upwardly through the base of the regenerator.

8j A Huid cracking unit comprising a regenerator provided with apluralityao'f regeneration zones, superposed one upon another; means forseparating an upper regeneration zone from a lower regeneration zone andpermitting movement of catalyst and regenerating gas therethrough; afirst reactor and a second reactor; means for removing a partiallyregenerated fluidized cracking catalyst from an upper regeneration zone,admixing it with a hydrocarbon charge stock containing appreciableamounts of deleten'- ous materials, and moving the resulting mixture tothe first reactor; means for removing a regenerated catalyst from alower regeneration zone, admixing it with a hydrocarbon charge stockcontaining substantially less of the objectionable materials than ispresent in the charge stock passed to the iirst reaction zone, andmoving the resulting mixture to the second reactor; means for removingracked products from each of the two reactors; means for continuouslyrecycling contaminated catalyst from each of the two reactors to anupper-,regeneration zone; and means for introducing an oxygen-containinggas upwardly through the base of the regenerator.

9. A fluid catalytic cracking unit in accordance with claim 8 in whichthe zones in the regienerator are separated by at least one grid.

10. A uid cracking unit intaccordance with claimV 8 in which theregenerator is provided with Vat least two regeneration zones.

ll. A fluid catalytic cracking unit in accordance with claim 8 in whichthe means for removing catalyst from the regeneration zones in theregenerator include standpipes extending upwardly through the baseof theregen- Y erator into the upper and lower regeneration zones, re-

spectively.

References Cited in the iile of this patent y UNITED STATES VPATENTS2,416,730 Arveson Mar. 4, 1947 2,432,644 Alther Dec. 16, 1947 2,444,990Hemminger Y July 13, 1948 2,465,255 Moorman Mar. 22, 1949 2,494,614Grote' Jan. 17, 1950

1. A FLUID CATALYTIC CRACKING PROCESS WHICH COMPRISES REGENERATINGCONTAMINATED FLUIDIZED CRACKING CATALYST PARTICLES BY REMOVING THECONTAMINANT BY OXIDATIVE COMBUSTION FROM THE CATALYST PARTICLES IN AREGENERATOR PROVIDED WITH A PLURALITY OF REGENERATION ZONE, SUPERPOSEDONE UPON ANOTHER, IN WHICH THE AMOUNT OF CONTAMINANT PRESENT ON THECRACKING CATALYST IN AN UPPER ZONE IS GREATER THAN THAT WHICH IS PRESENTON THE CRACKING CATALYST IN A LOWER ZONE THEREOF, THE AMOUNT OFCONTAMINANT IN SAID UPPER ZONE BEING ABOUT 0.4 TO ABOUT 1.0 WEIGHTPERCENT AND THE AMOUNT OF CONTAMINANT IN SAID LOWER ZONE BEING ABOUT 0.1TO ABOUT 0.6 WEIGHT PERCENT; ADMIXING A HYDROCARBON CHARGE STOCKCONTAINING APPRECIABLE AMOUNTS OF DELETERIOUS MATERIALS WITH PARTIALLYREGENERATED CRACKING CATALYST OBTAINED FROM AN UPPER REGENERATION ZONE;SUBJECTING SUCH MIXTURE TO RELATIVELY MILD CRACKING CONDITIONS IN AFIRST REACTION ZONE FOR A TIME SUFFICIENT TO RELEASE A MAJOR PORTION OFSAID DELEFERIOUS MATERIALS IN SAID FIRST REACTION ZONE AND DEPOSITCONTAMINANT ON THE CRACKING CATALYST THEREIN; ADMIXING A HYDROCARBONCHARGE STOCK CONTAINING SUBSTANTIALLY LESS OF THE DELETERIOUS MATERIALSTHAN IS PRESENT IN THE CHARGE STOCK PASSED TO FIRST REACTION ZONE WITH AREGENERATION CRACKING CATALYST OBTAINED FROM A LOWER REGENERATION ZONE;SUBJECTING SAID LAST NAMED MIXTURE TO ELEVATED TEMPERATURES IN A SECONDREACTION ZONE, THEREBY FORMING A RELATIVELY LOWER BOILING HYDROCARBONPRODUCT AND DEPOSITING CONTAMINANT ON THE CATALYST PARTICLES THEREIN;CONTINUOUSLY RECYCLING CONTAMINATED CATALYST FROM EACH OF THE TWOREACTION ZONES TO THE REGENERATOR AND CONTINUOUSLY WITHDRAWING THECRACKED PRODUCT FROM EACH OF THE TWO REACTION ZONES.